Repurposed and edited from a comment here

I can only speculate as to a slut's internal mental processes. From what I can see and deduce, it looks like a combination of genuine bewilderment, apex fallacy, revulsion to judgment, sensitivity to possible rejection, anti slut defense, and resentment at having to settle. Let me explain.

The first part of it is she really doesn't get why her having sex with a lot of guys before him is a big deal to him. To her, this is just part of life. You're a young unmarried person, you have fun and you enjoy your life, and you party hard. And sometimes that fun and enjoyment is casual sex. And sometimes you get into relationships of varying duration and intensity, and that includes sex.

Everyone she knows does it this way. All her friends do, both men and women (as far as she knows). Her girlfriends definitely do. And men must do it too. I mean, after all, it's men that her girlfriends are having all that sex with. That means lots of men are getting laid too. And she knows a lot of those men, because she's had sex with at least some of them too. She has known lots of guys growing up and in school, college, and young adult life. They have sex with multiple women.

I mean, what the hell is the big deal? Everyone is doing this, and it's OK. Why are you all bent out of shape that I had sex with a lot of guys? Guys are having sex with a lot of girls. I bet YOU had sex with a lot of girls. I cannot imagine that any man is out there not having sex!

Part of it is projection and solipsism. Women can get sex anytime they want. Sex is easy to get for them. It's also easy for them to get sex with the men they want, usually. It's also easy for them to get sex with men they are attracted to - some of them extremely physically attractive. (It is far, far more likely for a woman to have had a very satisfying sexual experience with a man she was really really attracted to hard, than it is for a man to have had a similar experience with a woman.) Since this is their experience, and because they're having sex with men, and because all the men and women they know are having sex, they conclude that this must also be the experience of most men, when it most definitely is NOT most men's experience.

It's partly apex fallacy. The men these women see and pay attention to are the top men, the most attractive men, the top 20% men. These are the men who are having most of the sex. And these are the only men they see - it's well known that women just don't pay any attention at all to men they aren't sexually attracted to. They don't even see or notice those bottom 80% men, or even acknowledge them as men.

It's partly feeling judgment and rejection - the two emotions women hate and fear the most. Women absolutely cannot handle negative judgment, and they just dissolve into puddles of raw emotion when rejected. And they really can't handle it when a man they perceive as a Beta Buck$ rejects them or tries to judge them. They are just not accustomed at all to mediocre men judging and rejecting them. They're accustomed to having mediocre men fall all over themselves just for a chance to carry her books or drive her someplace or loan her something.

And there's anti-slut defense. Not only is the BB judging her and rejecting her, he's judging and rejecting her for treating him differently from the other men she slept with. He is setting out, explicitly, that he has a problem with the different treatment, and that she gave it up rapidly to more attractive men, and makes him wait.

It's about her settling. It's about her having settled for this Beta Buck$ guy. She made him wait because she's not all that sexually attracted to him, which is a major reason why she made him wait weeks or months, whereas she didn't before. But secondarily, she made him wait so as to create the appearance of value - if you value her, you'll wait for her. Other men before wouldn't wait or would pump and dump it.

She also made him wait to see what kind of guy she's dealing with. When he waits, she knows she's dealing with a Beta Buck$ who she can manipulate, control, and mine for resources. It also means she can control the relationship - the sex, the pacing, the timing, the dynamics, and most of the interactions. This is why women like beta buck$ men - they're easier to control. It's also why women rear up against judgment and rejection from BBs. A BB who does that is trying to exert control, and it's both unexpected and "not permitted".

The alphas she's accustomed to fucking don't wait. If she won't fuck, there's 3 or 4 other girls in the rotation who will. If she makes him wait, she's out of the running for anything with Mr. Alpha. And she knows this - she knows that's the game and that's how it's played. And with alphas she has much less control over everything. Alphas can't be manipulated with sex, or overwrought emotional displays, or anything much, really. He can't be mined for resources because he's already made clear he won't give her any, and she's probably already fucked him for free. And she cannot control the pacing or timing as much with alphas.

And she does not like it that this Beta Buck$ guy, this less attractive mediocre guy she's trying to extract commitment from, whom she could manipulate and control with sex, is all of a sudden raising a stink about her having fucked 20 or 30 other guys. She settled for him. She did him a favor. And she's having it thrown in her face that this guy, who's now complaining, is the best she could do. She's facing up to the fact that she couldn't get any of those hot guys to give her the stuff she can so easily extract and cajole from Mr. Beta Buck$. And she couldn't, because she wasn't good enough or high value enough. And that really frosts her. Big time.